Solution of the10Li-Puzzle

The mass of¹⁰Li has been measured with two different reactions:⁹Be(¹³C,¹²N)¹⁰Li,E _Lab=336 MeV, and¹³C(¹⁴C,¹⁷F)¹⁰Li,E _Lab=337 MeV. The mass excess of 33.445(50) MeV is deduced from theQ-value measurement.¹⁰Li is found to be particle-unstable with respect to one-neutron emission by 0.42(5) MeV. In the analysis of the first reaction a low lying excited state is found at 0.38(8) MeV. This state and the ground state can be most probably identified as the 1⁺/2⁺-doublet coupled from the [π 1p3/2 ?ν 1p 1/2] configuration, the 1⁺-state being the ground state. The (¹³C,¹²N)-reaction populates the 1⁺-state strongly due to a spin-isospin-flip character of the dominant part of the transition amplitude. The 2⁺-member corresponds to the mass given by Wilcox et al. A second excited state is observed at 4.05(10) MeV with a width of 0.7(2) MeV, it can be associated with theν 1d 5/2-strength. The second reaction is fully supporting the interpretation of the ground state doublet. The excited state at 4.05 MeV is not observed in this reaction and indeed it should not, because the reaction does not populate in first order excited neutron configurations. The levels are well described by mean field calculations including pairing correlations. The lowest resonance in the calculations is theν 1/2^?-configuration, whereas theν 1/2⁺-configuration shows at the neutron threshold a strong non-resonant contribution.     

Three-particle correlations from208Pb+6Li

Three-particle correlations in the reaction²⁰⁸Pb+⁶Li were studied near the Coulomb threshold between \(E_{6_{Li} } = 24\) and 30 MeV. Three reaction mechanisms contribute predominantly to the observed coincidences of the charged particles: 1. Coulomb excitation of the 2.184 MeV,J=3⁺ state of⁶Li, followed by the decay intoα+d, 2. Deuteron pick-up of the⁶Li to the ground state of⁸Be and sequential decay into twoα-particles and 3. Neutron-transfer to the ground state and the first excited states of²⁰⁹Pb:²⁰⁸Pb(⁶Li,αp). The last two reaction mechanisms explain the previously measured large contributions to theα-channel relative to thed-channel.     

The low-lying level structure of87Rb

The low-lying states of⁸⁷Rb are studied in the framework of a quasiparticle-core coupling model. The agreement between the calculated and experimental level spectra, stripping strength, ground state static electromagnetic moments and theE2 transition rate of the first excited state is good. Electromagnetic moments and transition rates for other excited states are predicted.     

Path integral Monte Carlo calculations of4He and6Li

We have performed Monte Carlo calculations to estimate the exact energies of model problems for⁴He and theL=0,1, and 2 states of⁶Li. Using a Feynman path-integral expression for the imaginary-time evolution operator, we recast the ground state energy as a sum over histories, which are then sampled stochastically. Use of a trial wave function dramatically improves the efficiency of the Monte Carlo method. For a state-independent Malfliet-Tjon potential, together with the Coulomb interaction, we find a ground state energy of ?28.00+0.20 MeV for⁴He, and a degeneracy of theL=0,1, and 2 states in⁶Li at about ?59.65+-0.50 MeV. Density distributions for these nuclei are also calculated.     

TheEC-decay of170Tm

The spectrum ofK X-rays andγ-rays following the decay of¹⁷⁰Tm has been reinvestigated using a high resolution Si(Li) detector. The intensities of theEC-branches from the ground state of¹⁷⁰Tm to the ground state as well as to the first excited level in¹⁷⁰Er have been measured. The total intensity of theEC-decay is (0.25 ± 0.05)% of all¹⁷⁰Tm disintegrations with (0.18 ± 0.05)% leading to the ground state and (0.07±0.02)% leading to the first excited level of¹⁷⁰Er. The energy of the de-excitingγ-ray has been determined to (78.7±0.5) keV. Its intensity is (0.28 ± 0.06)% of that of the 84.3 keVγ-ray in¹⁷⁰Yb.     

Energy levels in46Ti

The gamma-ray spectra of several resonances in the⁴⁵Sc(p, γ)⁴⁶Ti reaction were measured using a 5 cm³ Ge(Li) detector. A thick target was bombarded with 1377 and 1660 keV protons, several resonances were therefore excited at each proton bombarding energy. The decay and energy of 30 excited levels were investigated. The intensity of all transitions to the ground state agrees within an error of about 9% with the total intensity of all transitions starting from the proton capture states, which indicates that low energy transitions between high-excited levels are of no importance. We have calculated a theoretical primary gamma-ray spectrum that fits the experimental averaged spectrum rather well.     

Intrastate γ-transitions: A spectroscopic tool?

In the framework of a potential model we have calculated the various bremsstrahlung cross sections into the⁵Li ground state, includingM 1 andE 2 γ-transitions leading from the high energy wing of the⁵Li ground state resonance into states belonging to the same resonance at lower energy (intrastate transition). Our calculation supports the hypothesis of Schmalbrock et al. [1] that intrastate transitions ofM 1 andE 2 multipolarity exist. While we find a maximum cross section of roughly 1.4 nb for theE 2 transition, we predict the cross sections forM 1 intrastate transition to be less than 3·10^?5nb. An experimental observation of the intrastate γ-ray emission appears to be very difficult due to the dominance of competing resonant (M 1) and direct (E 1) capture processes. Schmalbrock et al. have suggested to deduce magnetic dipole and electric quadrupole moments of resonant states from the measurements of the respectiveM 1 andE 2 intrastate transitions. We will show that theM 1 intrastate cross sections do not yield the appropriate information to determine the magnetic dipole moment. We will also discuss thatE 2 intrastate transitions do not seem to be a suited tool to find the quadrupole moment of an unstable state.     

Five-nucleon transfer in the12C(d,7Li)7be reaction atE lab=78.0 MeV

Angular distributions of the¹²C(d,⁷Li)⁷Be reaction to the ground and to the unresolved first excited states of⁷Li or⁷Be nuclei were measured in the entire angular region in the centre of mass system atE _lab=78.0 MeV. Both the one-step five-nucleon cluster transfer as well as two-step sequential transfers were considered in the theoretical analysis. The former mechanism was found to dominate, but the latter is also not negligible.     

(n, α) Reactions on light nuclei atE n =13.9 MeV

The reactions¹⁴N (n, α)¹¹B and¹⁰B(n, α)⁷Li were studied with 13.9 MeV neutrons using a counter telescope. Differential cross sections were measured for the transitions to the ground states and to some excited states. The results provide evidence for a strong contribution from a direct reaction mechanism. Systematics of integrated cross sections for the ground state transitions of all known (n, α) reactions on light nuclei with 14 MeV neutrons is also given.     

Isospin in halo nuclei: Borromean halo,tango halo,and halo isomers

It is shown that the wave functions for isobaric analog, double isobaric analog, configuration, and double configuration states may simultaneously have components corresponding to nn, np, and pp halos. The difference in the halo structure between the ground and excited states of a nucleus may lead to the formation of halo isomers. A halo structure of both Borromean and tango types can be observed for np configurations. The structure of ground and excited states with various isospins in halo-like nuclei is discussed. The reduced probabilities B(Mλ) and B(Eλ) for gamma transitions in ^6?8Li, ^8?10Be, ^8,10,11B, ^10?14C, ^13?17N, ^15?17,19O, and ¹⁷F nuclei are analyzed. Particular attention is given to the cases where the ground state of a nucleus does not have a halo structure, but where its excited state may have it.     

Study of the excited states of119Sn by the decay of119g+m In

The decay of^119g+m In to the excited states of¹¹⁹Sn was investigated.¹¹⁹In was produced by the¹²⁰Sn(γ,p)¹¹⁹In reaction on an enriched SnO₂ target. The isomeric transition of 311.25 keV to the¹¹⁹In ground state was observed. In the beta decay of^119m In excited states at 23.9, 920.5, 921.4, 1089.0, 1187.9 and 1249.6keV in¹¹⁹Sn withJ ^π values of 3/2⁺, 3/2⁺, 5/2⁺, 5/2⁺, 3/2⁺ and 1/2⁺ respectively, are fed. In the decay of the¹¹⁹In ground state only the 7/2⁺ level in¹¹⁹Sn at 787.0 keV is fed.     

The deformation of the ground and excited states in the Ag and Sn nuclei

The microscopic calculation of the potential energies in the ground and excited states of Ag and Sn nuclei has been performed. The single particle Nilsson potential and the shell correction Strutinski method have been used. The weak sensitivness to nonaxial deformation has been found for even neighbours of these nuclei. The small tendency towards prolate deformation of the ground and excited one-quasiparticle states originating from theg _9/2 proton subshell in^101–105Ag odd isotopes has been noticed. The behaviour with quadrupole e and hexadecapole ε₄ deformation of the ground and two-quasiparticle excited 0⁺ states originating from thed _5/2,g _9/2 andg _7/2 proton subshells andh _11/2 neutron subshell in^112–118Sn has been investigated. The small quadrupole deformation of the excited 0⁺ states has been found what is in agreement with the experimental data concerning the rotational bands build on the first excited 0⁺ states in Sn isotopes.     

The binary and ternary fission of thorium,lead and platinum induced by 12.2 GeV protons

We have investigated the decay of^123g+mIn to excited states of¹²³Sn.¹²³In was produced by the¹²⁴Sn(y,p)¹²³In reaction on an enriched SnO₂ target. The isomeric transition to the¹²³In ground state was not observed. In the beta decay of^123m In excited states at 24, 150.9, 920.5, 1194, 2621, 3151, 3256 and 3306 keV in¹²³Sn withJπ values 3/2⁺, 1/2⁺, (5/2⁺), 5/2⁺, 1/2⁺, (1/2⁺, 3/2⁺), 3/2⁺ and (l/2⁺, 3/2⁺), are fed. In the β decay of the¹²¹In ground state only the 7/2⁺ level at 1154 keV in¹²³Sn is observed.     

Nuclear field theory predictions for 11Li and 12Be: Shedding light on the origin of pairing in nuclei

Recent data resulting from studies of two-nucleon transfer reaction on ¹¹Li, analyzed through a unified nuclear-structure-direct-reaction theory have provided strong direct as well as indirect confirmation, through the population of the first excited state of ⁹Li and of the observation of a strongly quenched ground state transition, of the prediction that phonon-mediated pairing interaction is the main mechanism binding the neutron halo of the 8.5-ms-lived ¹¹Li nucleus. In other words, the ground state of ¹¹Li can be viewed as a neutron Cooper pair bound to the ⁹Li core, mainly through the exchange of collective vibration of the core and of the pigmy resonance arizing from the sloshing back and forth of the neutron halo against the protons of the core, the mean field leading to unbound two-particle states, a situation essentially not altered by the bare nucleon-nucleon interaction acting between the halo neutrons. Two-neutron pick-up data, together with (t, p) data on ⁷Li, suggest the existence of a pairing vibrational band based on ⁹Li, whose members can be excited with the help of inverse kinematic experiments as was done in the case of ¹¹Li(p, t)⁹Li reaction. The deviation from harmonicity can provide insight into the workings of medium polarization effects on Cooper-pair nuclear pairing, let alone specific information concering the “rigidity” of the N = 6 shell closure. Further information concerning these questions is provided by the predicted absolute differential cross sections σ _abs associated with the reactions ¹²Be(p, t)¹⁰Be(g.s.) and ¹²Be(p, t)¹⁰Be(pv) (≈¹⁰Be(p, t)⁸Be(g.s.)). In particular, concerning this last reaction, predictions of σ _abs can change by an order of magnitude depending on whether the halo properties associated with the d _5/2 orbital are treated selfconsistently in calculating the ground state correlations of the (pair removal) mode, or not.     

(p,t) Reaction studies on some even isotopes of samarium

The (p, t) reaction on the even isotopes¹⁴⁴Sm,¹⁴⁸Sm and¹⁵⁰Sm has been investigated at an incident proton energy of 25.5 MeV. Angular distributions have been measured for transitions to the ground state and excited states up to an excitation energy of about 2.5 MeV. Especially theL=0 angular distributions are discussed.     

The decay of121g+m In to levels in121Sn

The decay of¹²¹ g+m In to the excited states of¹²¹Sn was investigated.¹²¹In was produced by the¹²²Sn(γ,p)¹²¹In reaction on an enriched SnO₂ target. Strong indications of the isomeric transition of 321 keV to the¹²¹In ground state were found. In the beta decay of^121m In excited states at 60.1, 908.9, 1101.9, 1120.4, 1403.0, 2864.1, 3119.8 and 3228 keV in¹²¹Sn withJ ^π values 1/2⁺, 3/2(5/2)⁺, 3/2⁺, 5/2⁺, 5/2⁺ and 1/2⁺ or 3/2⁺ for the three levels around 3 MeV, are fed. In the decay of the¹²¹In ground state only the 7/2⁺ level in¹²¹Sn at 925.3 keV is fed.     

Structures and electronic states of photoexcited states in a system of two nitroxide radicals linked to fullerene studied by two-dimensional pulsed nutation and time-resolved electron paramagnetic resonance spectroscopy

Magnetic properties of fulleropyrrolidine adducts with two stable nitroxide radicals (2,2,6,6-tetramethylpiperidine-1-oxyl, TEMPO) were studied in toluene solution by continuous-wave time-resolved (TR) and pulsed electron paramagnetic resonance (EPR) spectroscopy in the ground and photoexcited states. Four isomers of the bisadduct,trans-1,trans-2,trans-3, and equatorial forms, having the second pyrrolidine ring at different [6-6] bonds were synthesized. In the ground states, the exchange interaction between two TEMPOs is so small that the spin state of the bisadduct is a doublet in nature. By means of spectral simulations of the EPR spectra in frozen solution at 70 K, the upper limit of the exchange interaction was estimated to be 5 MHz for thetrans-1 andtrans-2 and 10 MHz for thetrans-3 and equatorial isomers. The simulation was also made to determine relative positions of the two TEMPO groups with respect to the pyrrolidine ring. Photoexcited states of the bisadducts with excitation of the 532 nm laser pulse were studied in frozen toluene solution at 5–100 K by using two-dimensional (2-D) pulsed nutation EPR and TREPR. The spin multiplicity of the excited state was determined by the nutation frequency. All of the four bisadducts showed strong exchange couplings between two TEMPOs and fullerene triplet³C ₆₀ ^* , resulting in the generation of the excited quintet and triplet states. The excited triplet states have been observed and assigned for the first time in strongly coupled triplet-radical systems. The zero-field splittings of the quintet state determined from the 2-D nutation EPR spectra were analyzed as the sum of the spinspin interactions among the three paramagnetic centers, two TEMPOs and³C ₆₀ ^* . On the basis of these analyses, the spin distribution on the³C ₆₀ ^* part and the geometry of two TEMPOs are discussed.     

Investigating highly excited states of the 8Li isotope

Highly excited states of the ⁸Li isotope are sought in absorption reactions of π^? mesons stopped by ^10,11B isotopes. The ground and three excited states of the ⁸Li isotope are observed in inclusive measurements of reactions ¹⁰B(π^?, d)X and ¹¹B(π^?, t)X. The states with excitation energies E _x ≈ 8.7 and 10.1 MeV are observed for the first time in correlation measurements of reactions ¹⁰B(π^?, dt)X and ¹¹B(π^?, tt)X.     

The 28Si(7Li, 7Be)28Al reaction at 36 MeV

The ²⁸Si(⁷Li, ⁷Be)²⁸Al reaction has been investigated at E_7Li = 36 MeV. States and groups of states were observed up to 5.3 MeV excitation in the ²⁸Al+⁷Be system. Experimental angular distribution for unresolved doublets of states at ≈ 0.0 and 0.44 MeV excitation, corresponding to ⁷Be in its ground state (⁷Be₀) and first excited states (⁷Be₁) with ²⁸Al in its ground state (3⁺) and first excited state (0.031 MeV, 2⁺) are compared with microscopic distorted wave approximation calculations.     

Remeasurement of capture to positron decay ratios in22Na and65Zn and comparison with theory

In the decay of²²Na theEC/β ⁺ ratio for theβ-transition to the 1275 keV-level was measured to beEC/β ⁺=0.1050 (29). Single and coincidence counting was performed using a 16% Ge(Li) and an NaI well-type detector. For⁶⁵Zn theK/β ⁺ ratio for the ground state transitionK ₁/β ⁺=30.3 (10) was obtained using the same apparatus and in addition a 10 mm diam. × 5.4 mm Si(Li) detector. The results are compared with earlier experiments and with theory.